Stabilization of photographic emulsions sensitized with alkylene oxide polymers



polymers.

United States Patent Ofiice 2,995,444 Patented Aug. 8, 1961STABILIZATION F PHOTOGRAPHIC' EMUISIONS SENSITIZED WITH ALKYLENE OXIDEPOLY- MERS Fritz Derseh, Blnghamton, N.Y., assiguor to General Aniline &Film Corporation, New York, N.Y., a corporation of Delaware No Drawing.I Filed Sept. 26, 1957, Ser. No. 686,278

3 Claims. Cl 96-107) This invention relates to photographic emulsionsand in particular to light-sensitive silver-halide emulsions sensitizedwith alkylene oxide polymers and containing therein polyvinylp'yrrolidone as a stabilizer and antrfogging agent.

It is known that the sensitivity of photographic emulsions, i.e.,light-sensitive gelatino silver-halide emulsions can be increased byincorporating in said emulsions various alkylene oxide polymers whichact in a manner analogous to the allylthioureas, thiocyanates, sodiumthiosulfate, sodium hyposulfite, and the like, and in this connectionreference is made to US. Patents 2,400,532, 2,441,389 and 2,423,549.

It is likewise known that photographic emulsions containing theaforementioned alkylene oxide polymers as sensitizers have a greatertendency to become fogged when compared to. photographic emulsions thatare not so sensitized. This fogging tendency is particularly pronouncedwhen photographic film, coated with a lightsensitive silver-halideemulsion containing the above described alkylene oxide polymers, issubjected to such conditions as prolonged development and storage atexcessive temperatures and humidities. It, therefore, becomes necessaryto employ rather large quantities of antifoggants in order to overcomethe greater susceptibility to fogging of photographic emulsionssensitized with the alkylene oxide However, this remedy of usingexcessively high amounts of an 'foggants partly ofisets the speedadvantage gained from the alkylene oxide polymers in the first placewith the result that the net increase in sensitivity of suchphotographic emulsions is very slight.

It is accordingly an object of this invention to provide photographicemulsions with increased sensitivity.

Specifically, an object of-this invention is to provide improvedphotographic silver-halide emulsions sensitized with alkylene oxidepolymers and having low susceptibility to fogging on prolongeddevelopment and storage under conditions of high temperatures andhumidities.

Other objects will appear hereinafter as the description proceeds.

The foregoing objects are attained by bringing poly-N-vinyl-2-pyrrolidone into operative association with thephotographicemulsions stabilized with alkylene oxide polymers. Theresulting emulsions possess the higher sensitivity of emulsionscontaining the alkylene oxide polymers but without their high foggingtendencies.

That poly-N-vinyl-Z-pyrrolidone should inhibit or reduce fog is mostunusual since it is known that this substance, while increasing thespeed when used alone in photographic emulsion, has no efiect onreducing the fog. It would appear, therefore, that the combination ofpoly- N-vinyl-Z-pyrrolidone and alkylene oxide polymers co-act oroperate in a synergistic manner when grouped in a photographicsilver-halide emulsion, that is, the ethylene oxide polymers function aschemical sensitizers while the poly-N-vinyl-Z-pyrrolidone prevents thefogging resulting as a side effect of the sensitizers.

It is to be understood, however, that the above explanation is merelyoffered as a theory to explain the mode of operation of this inventionand is not to be construed as imposing a limitation or narrowingthereof.

so-called sulfur sensitizers such as porated at any convenient timeduring the preparation of the silver-halide emulsion, it is preferred toadd it shortly before coating. Themost useful concentrations of poly-N-vinyl-Z-pyrrolidone ranges from 2 to 25 g. per mole of silver-halidein the emulsion; optimum concentration is about 6 g. of the stabilizerper mole of silver-halide.

The poly-N-vinyl-Z-pyrrolidone as used herein is a product of theGeneral Aniline and Film Corporation and is sold under the name of PVP,type NP (nonpharmaceutical) and is available in viscosities of K-20,K-30 and K-40, all of which are suitable for use as a stabilizer in thepresent invention. The letter K represents a function of the meanmolecular weight of the compound and is derived from the Fikentscherformula wherein c is the concentration in g./- ml. of solution, a is theviscosity of the solution compared to the solvent and K=1000K Thealkylene oxide polymers are known chemical substances and many arecommercially available. They can be prepared in various ways. Forinstance, a common procedure is to react an alkylene oxide such asethylene oxide, propylene oxide, butylene oxide, etc., with polyhydricalcohols such as ethylene glycol, diethylene glycol, nonaethyleneglycol, decaethylene glycol, dodecaethylene glycol, ring dehydrationproducts of hexitols, etc. For additional information on the preparationof the above substances, reference is'made to The Chemistry of SynthetioResins, pages 990-994, published by Reinhold Publishing Corporation(1935).

In general, the aforementioned poly-N-vinyl-2-pyrrolidone is useful forstabilizing all types of photographic silver-halide emulsions sensitizedwith alkylene oxide polymers. However, it has been found that superiorresults ensue when my stabilizer is incorporated in emulsions sensitizedwith alkylene oxide polymers of the class described in the previouslycited patents. These alkylene oxide polymers are polyglycols and areprepared by re-' acting alkylene oxides with polyhydric alcohols, suchas glycols, until the products have a molecular weight in excess of 300,preferably of 1500 or 4000 or more. The resulting polyglycols can befurther modified by reacting with various mono-functional etherificationor ester-ification agents to introduce lipophilic groups, e.g., analiphatic hydrocarbon chain of 8 to 18 or more carbon atoms such asn-octyl, n-dodecyl, n-tetradecyl, n-octadecyl, and the like, and a fattyacid halide of 8 to 20 carbon atoms such as noctadecoyl, n-dodecoyl,n-tetradecoyl,

of aqueous salts usually by washing, (3) the second diges-.

tion or after-ripening to obtain increased sensitivity.

The combination of polyalkylene oxide polymers as stabilizers andpoly-N-vinyl-Z-pyrrolidone as an antifoggant for photographicsilver-halide emulsions are effectual in the presence or absence ofoptical sensitizing dyes, color formers, or other addenda commonlyincorporated in photographic emulsions.

My invention is not limited to silver-halide emulsions wherein thecarrier is gelatin but may be incorporated with other light-sensitivematerials wherein the carrier can be polyvinyl alcohol, casein, carboxymethyl cellulose, and the like- The invention is illustrated in greaterdetail but not limited or restricted by the following example.

A silver-halide emulsion in gelatin containing 4% silver iodide and 96%silver bromide was prepared in a conventional manner and brought up toits maximum light sensitivity. It was then readied for coating, finalswere added such as sensitizing dyes, stabilizers and hardeners. A 10%solution of polyethylene oxide lauryl ether (a product sold by the AtlasPowder Company, Wilmington, Delaware, under the trade name BRII 35") inwater was prepared and added to the emulsion. Also, a 25% aqueoussolution of PVP (NP: K-30) was prepared and added to the emulsion. Theemulsion samples contained about 0.4 mole of silver-halide. The soprepared emulsion samples were coated on a suitable cellulose ester baseand dried. Samples of these film coatings were then ex- 35 is in I 5:3if the 321 223mm. deYeloped m a References Cited in the file of thispatent G, UNITED STATES PATENTS 1.5 2,423,549 Blake et aL my 1947 Mumwlfits, anhydrous 45 4; 2,495,918 301 1m 31, .1950 mm biwlfifi 12,712,995 Weyde My 12, 1955, Hydroquinone 3 Sodium carbonate,monohydrated. 6 FOREIGN PATENTS Potassium bromide 8 687,751 GreatBritain Feb. 18, 1953 Water to make 1 liter.

I claim:

-1. A photographic element comprising a support, at least onelight-sensitive silver-halide emulsion layer comprising a silver-halidedispersed in a colloidal carrier selected from the class consisting ofgelatin, polyvinyl alcohol, casein, and carboxy methyl cellulose, saidemulsion layer containing in intimate contact with the silver halidegrains thereof, a sensitizing quantity of an alkylene oxide polymerhaving a molecular weight of at least 300 and being selected from thegroup consisting of a polyalkylene glycol, a polyalkylene glycol etherwherein the ether group is an aliphatic chain of from 8 to 18 carbonatoms and a polyalkylene glycol ester wherein the ester group is analiphatic chain of from 8 to 18 carbon atoms and as' an antifoggingagent for said emulsion layer and in intimate contact with the silverhalide. grains thereof 2 g. to g. per mole of silver-halide in theemulsion of poly-N-vinyl-Z-pyrrolidone having a K-value of from in thecolloidal carrier for the light-sensitive silver-halide

1. A PHOTOGRAPHIC ELEMENT COMPRISING A SUPPORT, AT LEAST ONELIGHT-SENSITIVE SILVER-HALIDE EMULSION LAYER COMPRISING A SILVER-HALIDEDISPERSED IN A COLLOIDAL CARRIER SELECTED FROM THE CLASS CONSISTING OFGELATIN, POLYVINYL ALCOHOL, CASEIN, AND CARBOXY METHYL CELLULOSE, SAIDEMULSION LAYER CONTAINING IN INTIMATE CONTACT WITH THE SILVER HALIDEGRAINS THEREOF, A SENSITIZING QUANTITY OF AN ALKYLENE OXIDE POLYMERHAVING A MOLECULAR WEIGHT OF AT LEAST 300 AND BEING SELECTED FROM THEGROUP CONSISTING OF A POLYALKYLENE GLYCOL, A POLYALKYLENE GLYCOL ETHERWHEREIN THE ETHER GROUP IS AN ALIPHATIC CHAIN OF FROM 8 TO 18 CARBONATOMS AND A POLYALKYLENE GLYCOL ESTER WHEREIN THE ESTER GROUP IS ANALIPHATIC CHAIN OF FROM 8 TO 18 CARBON ATOMS AND AS AN ANTIFOGGING AGENTFOR SAID EMULSION LAYER AND IN INTIMATE CONTACT WITH THE SILVER HALIDEGRAINS THEREOF 2G. TO 25G. PER MOLE OF SILVER-HALIDE IN THE EMULSION OFPOLY-N-VINYL-2-PYRROLIDONE HAVING A K-VALUE OF FROM K-20 TO K-40.